Adequate platelet inhibition with dual antiplatelet therapy is a key therapeutic goal after primary percutaneous coronary intervention (PPCI), aimed at protecting against stent thrombosis and increased mortality. Recent aggregometric assays have shown that up to one third of acute coronary syndrome patients treated with clopidogrel have incomplete inhibition of adenosine diphosphate(ADP)-induced platelet aggregation while the number of patients treated with aspirin who have incomplete inhibition of thromboxane A2-induced platelet aggregation (ASPI)is much lower. High on-treatment platelet reactivity (HTPR) has been associated with an increased rate of ischemic events after PCI. However, recent large trials did not show a clinical benefit of TPR-guided therapy modification in acute coronary syndrome patients treated by PCI.